In an exemplary application, polymer electrolyte fuel cells (PEFCs) are currently under development to produce electrical power for a variety of stationary and transportation applications. To produce useful currents and voltages, individual fuel cells are connected in series to form stacks of cells. Adjacent cells in a stack are typically separated by bipolar plates, which serve as the anode for one fuel cell and the cathode for the adjacent cell. Thus the bipolar plate must function as a current collector as well as an impermeable barrier between the gases on either side of the plate. In addition, many stack designs incorporate gas flow channels into the bipolar plate. These flow fields ideally provide equal distribution of reactant gases over the entire area of a catalyzed proton exchange membrane. Flow fields are commonly molded or machined into both sides of a bipolar plate, with an anode flow field on one side and a cathode flow field on the other side.
To date, the bipolar plate remains the most problematic and costly component of PEFC stacks, as well as other electrochemical cells, such as alkaline fuel cells, zinc-air batteries, and the like. The most commonly used material for single cell testing is machined graphite, which is expensive and costly to machine. The brittle nature of graphite also prevents the use of thin components for reducing stack size and weight, which is particularly important for transportation applications. Other stack designs consider the use of metal hardware such as stainless steel. But a number of disadvantages are associated with stainless steel, including high density, high cost of machining, and possible corrosion in the fuel cell environment. Still other designs use graphite/poly(vinylidene fluoride) composites, which can be relatively brittle and expensive and require long process cycle times. Attributes of a suitable material include:
i) high electronic conductivity; PA1 ii) low weight; PA1 iii) low permeability; PA1 iv) physical and chemical stability under fuel cell operating conditions PA1 v) low cost of mass production.